Vas

VAS (Latin vessel), a designation for blood vessels and tubular structures serving to discharge organ secretions from the body, or from one organ to another. Examples: Vas aberrantia—vessels connecting the brachial artery (a. brachialis) with one of the forearm arteries (usually the a. radialis), which are anomalies of the vascular system; Vas afferentia—lymphatic vessels flowing into lymph glands; Vas efferentia—lymphatic vessels emerging from them. Vas deferens, the excretory duct of the testis (spermatic duct), is a continuation of the epididymis (detailed—see Spermatic cord). Vasa vasorum, vessels of vessels, otherwise vasa nutritia, nourishing vessels, are present in the walls of all larger vessels, arteries, and veins, beginning approximately with a diameter of 1 mm and ending with the aorta. They never originate from the nourished vessel itself, but from neighboring ones or from its smaller branches. The walls of the aorta are supplied from branches of the intercostal and lumbar arteries, with them branching [Transverse section of a large caliber artery (elastic type): a-inner coat; b-middle; c-outer; d-vessel nourishing the outer on the aorta, embracing it like a to-, like the branches of the mesenteric artery] embrace the outer coat of the intestine. Arterioles entering the vessel usually branch in its outer connective-tissue coat (adventitia), and in rarer cases extend into the middle muscular coat (media), usually limiting themselves to its outer layers, but vasa vasorum have also been described in the inner coat—intima (inferior vena cava of an ox).

Arterial trunks are usually accompanied by two venous ones, which, in the case of an artery, flow into neighboring veins, and in a vein directly into its lumen. As a rule, veins contain more vasa vasorum than arteries, and vasa vasorum penetrate deeper into them. Lymphatic vessels have also been described in the outer coat of muscular-type arteries, and in veins devoid of muscles—throughout the entire wall. Schifferdecker discovered lymphatic capillaries right beneath the endothelium in the aorta of a pig using the silvering method. Vasa nervorum are arterioles nourishing a nerve. Every nerve, superficial and deep, is accompanied by an artery (satellite artery), from which smaller arteries depart at an acute angle, heading toward the nerve, on the surface of which they divide into two branches—descending and ascending, anastomosing with corresponding neighboring arteries. The number of arteries and the places of their penetration into the nerve are constant for the same nerve, whereas the branching methods are diverse. An anastomosis exists between the arteries both inside the nerve. From these anastomotic arches, arterioles depart in a fan-like manner, which, gradually decreasing in caliber, pass into the perineurium, where they divide into thin capillaries penetrating already into the nerve bundle itself.